pgfplots - Placing Nodes on x Coordinates of a Plot

Question

I want to plot some graphs in pgfplots and want to place nodes on the exact same x coordinate of the plot. The position of the note has to be set in x direction but free in y direction. Here is one example of the way it shouldn't be.

\documentclass{article}
\usepackage{pgfplots}

\begin{document}

\begin{figure} 
\begin{tikzpicture}    
\begin{axis}
    \addplot {-x}  [yshift=8pt] node[pos=0.1] {$0,1$};
    \addplot {x^2} [yshift=8pt] node[pos=0.1] {$0,1$};
    \addplot{3*x^2}[yshift=8pt] node[pos=0.1] {$0,1$};
\end{axis} 
\end{tikzpicture} 
\end{figure}

\end{document}

---

With the example linked by Jake I adapted the file. Now it is producing the return value 1 and no good result. What is wrong?

\documentclass{article}
\usepackage{pgfplots}

\begin{document}

\begin{figure} 
\begin{tikzpicture}    
\begin{axis}
\addplot[yshift=8pt,add node at x={-4}{$0,1$}] {-x};
\addplot[yshift=8pt,add node at x={-4}{$0,1$}] {x^2};
\addplot[yshift=8pt,add node at x={-4}{$0,1$}] {3*x^2};
\end{axis} 
\end{tikzpicture} 
\end{figure}

\end{document}

Answer 1

You can use the code from the answer to pgfplots: Placing node on a specific x-position:

\documentclass{article}
\usepackage{pgfplots}
\usetikzlibrary{intersections}

\makeatletter
\def\parsenode[#1]#2\pgf@nil{%
    \tikzset{label node/.style={#1}}
    \def\nodetext{#2}
}

\tikzset{
    add node at x/.style 2 args={
        name path global=plot line,
        /pgfplots/execute at end plot visualization/.append={
                \begingroup
                \@ifnextchar[{\parsenode}{\parsenode[]}#2\pgf@nil
            \path [name path global = position line #1-1]
                ({axis cs:#1,0}|-{rel axis cs:0,0}) --
                ({axis cs:#1,0}|-{rel axis cs:0,1});
            \path [xshift=1pt, name path global = position line #1-2]
                ({axis cs:#1,0}|-{rel axis cs:0,0}) --
                ({axis cs:#1,0}|-{rel axis cs:0,1});
            \path [
                name intersections={
                    of={plot line and position line #1-1},
                    name=left intersection
                },
                name intersections={
                    of={plot line and position line #1-2},
                    name=right intersection
                },
                label node/.append style={pos=1}
            ] (left intersection-1) -- (right intersection-1)
            node [label node]{\nodetext};
            \endgroup
        }
    }
}

\begin{document}

\begin{figure} 
\begin{tikzpicture}    
\begin{axis}
\addplot[add node at x={-4}{[fill=white]{$0,1$}}] {-x};
\addplot[add node at x={-4}{[fill=white]{$0,1$}}] {x^2};
\addplot[add node at x={-4}{[fill=white]{$0,1$}}] {3*x^2};
\end{axis} 
\end{tikzpicture} 
\end{figure}

\end{document}